1. Field of the Invention
The present invention relates to a toroidal type continuously variable transmission which can be used to a transmission for an automobile and various industrial machines.
2. Description of the Background Art
For example, a double-cavity-type toroidal type continuously variable transmission used as a transmission for an automobile is structured as shown in FIGS. 3 and 4. As shown in FIG. 3, inside a casing 50, there is supported an input shaft (center shaft) 1 in such a manner that it can be rotated. On the outer periphery of the input shaft 1, there are mounted two input side disks 2, 2 and two output side disks 3, 3. Also, on the outer periphery of the middle portion of the input shaft 1, there is rotatably supported an output gear 4. The output gear 4 includes in the central portion thereof cylindrical-shaped flange portions 4a, 4a which are respectively connected to the output side disks 3, 3 through spline engagement.
The input shaft 1 can be driven and rotated by a drive shaft 22 through a loading-cam-type pressing device 12 interposed between a cam plate 7 and the input side disk 2 that is positioned on the left side in FIG. 3. Also, the output gear 4 is supported within the casing 50 through a partition wall 13 constructed by connecting two members to each other, whereby the output gear 4 can be rotated about the center axis O of the input shaft 1 but it is prevented from shifting in the direction of the center axis O.
The output side disks 3, 3 are respectively supported by needle bearings 5, 5 respectively interposed between the input shaft 1 and the respective disks in such a manner that they can be rotated about the center axis O of the input shaft 1. Also, the input side disk 2 shown on the left side in FIG. 3 is supported on the input shaft 1 through a ball spline 6 and the input side disk 2 shown on the right side in FIG. 3 is spline connected to the input shaft 1, while these two input side disks 2 can be rotated together with the input shaft 1. Further, between the inner surfaces (concave-shaped surfaces) 2a, 2a of the input side disks 2, 2 and the inner surfaces (concave-shaped surfaces) 3a, 3a of the output disks 3, 3, there are held power rollers 11 (see FIG. 4) in such a manner that they can be rotated.
On the inner peripheral surface 2c of the input side disk 2 positioned on the right side in FIG. 3, there is provided a stepped portion 2b against which a stepped portion 1b provided on the outer peripheral surface 1a of the input shaft 1 is butted, while the back surface (the right surface in FIG. 3) of the input side disk 2 is butted against a loading nut 9. This substantially prevents the input side disk 2 from shifting from the input shaft 1 in the center axis O direction. Also, between the cam plate 7 and the collar portion 1b of the input shaft 1, there is interposed a counter sunk spring 8 which applies a pressing force to contact portions where the concave-shaped surfaces 2a, 2a, 3a, 3a of the respective disks 2, 2, 3, 3 and the peripheral surfaces 11a, 11a of their corresponding power rollers 11, 11 are contacted with each other.
Now, FIG. 4 is a section view taken along the line A-A shown in FIG. 3. As shown in FIG. 4, inside the casing 50, there are provided a pair of trunnions 15, 15 which can be swung about a pair of pivot shafts 14, 14 torsionally positioned with respect to the input shaft 1. Here, in FIG. 4, the illustration of the input shaft 1 is omitted. The respective trunnions 15, 15 include, in the two end portions thereof in the longitudinal direction (in FIG. 4, in the vertical direction) of their respective support plates 16, a pair of bent wall portions 20, 20 which are formed so as be bent in the direction of the inner surface side of the support plates 16. Thanks to the formation of these bent wall portions 20, 20, in the respective trunnions 15, 15, there are formed concave-shaped pocket portions P which are used to store their respective power rollers 11 therein. Also, on the outer surfaces of the respective bent wall portions 20, 20, there are provided the pivot shafts 14, 14 such that they are concentric with each other.
In the central portion of each support plate portion 16, there is formed a circular hole 21; and, in the circular hole 21, there is supported the base end portion (first shaft portion) 23a of a shift shaft 23. And, if the trunnions 15, 15 are respectively swung about their respective pivot shafts 14, 14, the inclination angles of the shift shafts 23 supported on the central portions of the respective trunnions 15, 15 can be adjusted. Also, on the peripheries of the leading end portions (second shaft portions) 23b of the shift shafts 23 projected out from the inner surfaces of the respective trunnions 15, 15, there are respectively supported the power rollers 11, 11 in such a manner that they can be rotated; and, the power rollers 11, 11 are respectively held between the input side disks 2, 2 and output side disks 3, 3. Here, the base end portions 23a and leading end portions 23b of the respective shift shafts 23, 23 are eccentric to each other.
Also, the pivot shafts 14, 14 of the respective trunnions 15, 15 are supported in such a manner that they can be swung with respect to a pair of yokes 23A, 23B and can be shifted in the axial direction thereof (in the front and back direction in FIG. 3, in the vertical direction in FIG. 4); and, the movements of the trunnions 15, 15 in the horizontal direction thereof are restricted by their respective yokes 23A, 23B. The yokes 23A, 23B are respectively formed into a rectangular shape by press working or forging metal such as steel. Each of the yokes 23A, 23B includes in the four corners thereof four circular support holes 18, and the four pivot shafts 14 disposed on the two end portions of the trunnions 15 are respectively supported on the four holes 18 in such a manner that they can be swung. In the central portions of the yokes 23A, 23B in the width direction thereof (in the right and left direction in FIG. 3), there are formed circular-shaped securing holes 19. The inner peripheral surfaces of the securing holes 19 are formed as spherically concave-shaped surfaces, while spherical surface posts 64, 68 are respectively fitted into the spherically concave-shaped surfaces of the securing holes 19. That is, the upper yoke 23A is swingably supported by the spherical surface post 64 which is supported on the casing 50 through a fixing member 52, while the lower yoke 23B is swingably supported by the spherical surface post 68 and the upper cylinder body 61 of a cylinder 31 supporting the spherical surface post 68.
Here, the shift shafts 23, 23 disposed on the respective trunnions 15, 15 are set in positions which are present 180 deg. opposite each other with respect to the input shaft 1. The direction, in which the leading end portions 23b of the respective shift shafts 23, 23 are eccentric to the base end portions 23a, is the same direction (in the reversed vertical direction in FIG. 4) with respect to the direction of rotation of the input side and output side disks 2, 2, 3, 3. Also, the eccentric direction is a direction which is substantially perpendicular to the direction of disposition of the input shaft 1. Thus, the respective power rollers 11, 11 are supported in such a manner that they can be shifted to some extent in the longitudinal direction of the input shaft 1. As a result of this, even when the respective power rollers 11, 11 tend to shift in the axial direction of the input shaft 1 due to the elastic deformation or the like of the respective composing members caused by a thrust load produced by the pressing device 12, unreasonable forces are not applied to the respective composing members but the shifting motion of the power roller 11 can be absorbed.
Also, between the outer surfaces of the respective power rollers 11 and the inner surfaces of the respective support plate portions 16 of the trunnions 15, in order starting from the outer surfaces of the power rollers 11, there are interposed thrust ball bearings 24 consisting of thrust ball-and-roller bearings and thrust needle bearings 25. Of these elements, the thrust ball bearings 24 not only support thrust-direction loads applied to the respective power rollers 11 but also allow the power rollers 11 to rotate. Each of the thrust ball bearings 24 consists of two or more balls 26, 26, an annular-shaped retainer 27 for retaining the respective balls 26, 26 in such a manner that the balls 26, 26 are free to roll, and an annular-shaped outer race 28. Also, the inner race tracks of the thrust ball bearings 24 are formed on the outer surfaces (large end faces) of their respective power rollers 11, while the outer race tracks of the ball bearings 24 are formed on the inner surfaces of their respective outer races 28.
Each thrust needle bearing 25 is held between the inner surface of the support plate portion of its corresponding trunnion 15 and the outer surface of the corresponding outer race 28. The thus-arranged thrust needle bearings 25 not only support thrust loads applied to the respective outer races 28 from their corresponding power rollers 11 but also allow the power rollers 11 and outer races 28 to swing about the base end portions 23a of the respective shift shafts 23.
On the one-end portions (lower end portions in FIG. 4) of the respective trunnions 15, 15, there are respectively disposed drive rods (trunnion shafts) 29, 29, while drive pistons (oil pressure pistons) 33, 33 are fixedly secured to the outer peripheral surfaces of the middle portions of the respective drive rods 29, 29. And, the drive pistons 33, 33 are respectively fitted in an liquid tight manner into the drive cylinder 31 consisting of the upper cylinder body 61 and lower cylinder body 62. The drive pistons 33, 33 and drive cylinder 31 constitute a drive unit 32 which can shift the respective trunnions 15, 15 in the axial directions of the pivot shafts 14, 14 of these trunnions 15, 15.
In the case of the thus-structured toroidal type continuously variable transmission, the rotation of the input shaft 1 is transmitted through the pressing device 12 to the respective input side disks 2, 2. And, the rotational movements of these input side disks 2, 2 are then transmitted through the pair of power rollers 11, 11 to the respective output side disks 3, 3; and, further, the rotational movements of the output side disks 3, 3 are taken out from the output gear 4.
To change a rotation speed ratio between the input shaft 1 and output gear 4, the pair of drive pistons 33, 33 may be shifted in the mutually opposing directions. When the respective drive pistons 33, 33 are shifted in this manner, the pair of trunnions 15, 15 are shifted in the mutually opposing directions. For example, the power roller 11 shown on the left side in FIG. 4 is shifted downward in FIG. 4, whereas the power roller 11 shown on the right side in FIG. 4 is shifted upward in FIG. 4. This changes the directions of tangential-direction forces applied onto the contact portions between the peripheral surfaces 11a, 11a of the respective power rollers 11, 11 and the inner surfaces 2a, 2a, 3a, 3a of the input side disks 2, 2 and output side disks 3, 3. With the change in the directions of the forces, the respective trunnions 15, 15 are swung in the mutually opposing directions about the pivot shafts 14, 14 which are pivotally supported on the yokes 23A, 23B.
This changes the contact positions between the peripheral surfaces 11a, 11a of the respective power rollers 11, 11 and the corresponding inner surfaces 2a, 3a, which then changes the rotation speed ratio between the input shaft 1 and output gear 4. Also, when the torque to be transmitted between the input shaft 1 and output gear 4 varies to thereby change the quantities of elastic deformation of the respective composing members, the respective power rollers 11, 11 and the outer races 28, 28 belonging to these power rollers 11, 11 are rotated slightly about the base end portions 23a, 23a of the respective shift shafts 23, 23. Such rotational movements are executed smoothly because the thrust needle bearings 25, 25 are present between the outer surfaces of these outer races 28, 28 and the inner surfaces of the support plate portions 16 constituting the respective trunnions 15, 15. This can reduce a force which is used to change the inclination angles of the respective shift shafts 23, 23 in such a manner as described above.
Now, in the thus-structured toroidal type continuously variable transmission, power is transmitted through the shearing force of oil (traction oil) existing between the input and output side disks 2, 3 and their corresponding power rollers 11 (between traction surfaces (rolling surfaces)) (see e.g. Japanese Patent Unexamined Publications No. JP-A-2003-343675 and JP-A-2003-278869). Because the coefficient of traction oil is fixed, to transmit high torque, a large load (pressing force) must be applied to the contact points between the input side and output side disks 2, 3 and power rollers 11.
A method for applying the above load includes a case using the before-described pressing device 12 of a loading cam type which mechanically generates a load in proportion to input torque, and a case using a pressing device of a hydraulic pressure type. In the case where only the pressing device 12 of a loading cam type, there is generated a thrust force (the pressing force of the input side disk) in proportion only to the input torque; and, therefore, depending on the transmission gear ratios, there is a fear that an excessive pressing force can act on the contact portions between the disks and rollers to thereby reduce the transmission efficiency and durability of the composing members. On the other hand, when the pressing device of hydraulic pressure type is used, the optimum pressing force can be applied in compliance with the transmission gear ratios, oil temperatures, numbers of revolutions and the like, which makes it possible to enhance the transmission efficiency and durability of the transmission when compared with the pressing device of a loading cam type.
Now, in order to widen the transmission range and disuse a starting device, there is conventionally known a transmission which is a combination of a toroidal type continuously variable transmission and a planetary gear mechanism and is capable of switching speed modes over to each other (that is, includes two or more speed modes).
In the above-mentioned transmission including a planetary gear mechanism, there occurs torque reversal at the mode switching areas, which makes it easy to cause torque shift (a phenomenon in which the power roller 11 is out of its center axis and thus slips sideways to thereby shift the set transmission gear ratio). This torque shift is caused by a difference in transformation between the composing members due to variations in the pressing force or by the rickety motion and worsened rigidity of the trunnions and power rollers due to variations in the traction force. When such torque shift is produced, in the mode switching time, a shock is given to the transmission and thus an automobile carrying the transmission on board, which reduces the riding feeling of the automobile. Also, when sudden torque shift occurs, there is a possibility that inconveniences such as a gross slip can be produced.
However, in the low speed time, due to the contact radius and transmission torque between the input side disk and power roller, there is required a high pressing force (in a toroidal type continuously variable transmission, the contact radius between the disk and power roller varies in accordance with transmission gear ratios and thus the necessary pressing force varies). Therefore, the surface pressure of the contact portion between the disk and power roller (in the case of a half toroidal type continuously variable transmission, the surface pressure of the power roller 1011 as well) becomes high, which has ill effects on the durability of the composing parts. Also, when the durability of the composing parts is raised, they become large in size.